Centrifugal buoyancy effect on heat transfer in a rotating two-pass rib-roughened channel with 180degrees sharp turns was numerically investigated by using the large eddy simulation. The effect of the aiding and opposing buoyancy contributions was seen in the suppressed turbulent transport in the radially inward flow, and in larger buoyancy-induced variation of the heat transfer on the pressure surface than that on the suction surface. As the buoyancy increased, the friction factor dominated by the pressure loss of the sharp turn decreased, and Colburn's j factor stayed almost constant. As a result, the heat transfer efficiency index slightly increased by the buoyancy, and it showed almost the same values among the three tested rib arrangements. (C) 2004 Elsevier Ltd. All rights reserved.